Field of the Invention
The present invention relates to an electrostatically operating microrelay, which can be used as a switch and which can be produced by the methods of micromechanics.
Electrostatic microswitches are ideally suited and distinctly superior to other semiconductor switches as far as attenuation and noise characteristics are concerned, in particular for applications in the radio-frequency range. A major advantage of switches of that type is that, apart from capacitive charging currents, powerless control of the switching contacts is possible. Electrostatic switches with a small switching time in a range below 100 xcexcs can only be realized by conventional methods if very great switching voltages can be accepted. It is generally the case with known ways of accomplishing the same that a compromise has to be made between the switching speed and the required switching voltage, since the rigidity of the resilient suspension of the switching element has the effect of requiring high switching voltages for high switching speeds. Battery voltages of at most 3 V are typically available, especially for use in cell phones. Switching voltages of at most 12 V are achievable by using voltage multipliers. Micromechanical switches are usually formed by micromechanically producible bars, at the end of which the switching contacts are disposed and which can be bent by electrostatic attraction through the use of electric potentials on suitably attached electrodes, in order to close the contacts. Electric voltages of typically 30 V and more are required in the case of switching times of 20 xcexcs. Therefore, those components are unsuitable for use in cell phones or other low-power applications.
In German Patent DE 41 13 190 C1 there is a description of an electrostatically actuated microswitch, in which an armature part constructed as a rocker has an armature spaced apart from a force electrode that is disposed on a base and is provided with two switching contacts on mutually opposite sides. When the device is actuated, those switching contacts alternately short two pairs of counterelectrodes provided as switches, which are disposed on the base.
In German Patent DE 198 23 690 C1 there is a description of a micromechanical electrostatic relay, in which a rib-shaped armature pivotably suspended in the region of a central pivot axis through the use of flexible bands is formed in an armature substrate. The armature forms an armature wing on each side of the pivot axis. The armature wing is in itself flexible and, in its inoperative state, is bent away from the base substrate, rolls on a base electrode and closes an associated contact when the device is actuated.
In German Patent DE 198 20 821 C1 there is a description of an electromagnetic relay which has a rocking armature with an armature plate, that is suspended in such a way that it can pivot transversely to the longitudinal direction of the armature plate through the use of two torsion springs, which are connected by a holding plate. The torsion springs and the holding plate provided for fastening the rocking armature are disposed in an inner recess of the armature plate.
In German Patent DE 42 05 340 C1 there is a description of a micromechanical, electrostatic relay in which an armature substrate within a frame carries a plate-shaped armature through the use of flexible supporting strips. In that way, an armature electrode provided on the armature is face-to-face with a base electrode and the armature is kept parallel to the base electrode through the use of the supporting strips and, when a voltage is applied between the armature electrode and the base electrode, comes to bear against the base electrode over its full surface area perpendicularly to the plane of the electrodes.
In a publication entitled xe2x80x9cMicromechanical Switches Fabricated Using Nickel Surface Micromachiningxe2x80x9d by P. M. Zavracky et al. in the Journal of Microelectromechanical Systems 6, 3-9 (1997), a description is given of micromechanical switches in which terminal contacts to be connected to one another in an electrically conducting manner are shorted through the use of a switching contact attached to a bar when the bar is bent toward the substrate by electrostatic force. That is accomplished by applying a voltage between the electrically conducting bar and a counterelectrode on the substrate.
In a publication entitled xe2x80x9cMicromechanical Relay with Electrostatic Actuationxe2x80x9d by I. Schiele et al. in Transducers ""97, 1997 International Conference on Solid-State Sensors and Actuators, Chicago, pages 1165-1168, a description is given of a microrelay in which, for closing the switch, a bar capable of bending is likewise electrostatically drawn toward the substrate and in which there is a T-shaped metallic lug on the bar for shorting the terminal contacts to be connected to one another in an electrically conducting manner. The lug is electrically insulated from the rest of the bar.
In a publication entitled xe2x80x9cDesign and Fabrication of Micro Mirror Supported by Electroplated Nickel Postsxe2x80x9d by Seok-Whan Chung et al. in Transducers ""95 Eurosensors IX, Proceedings of the 8th International Conference on Solid-State Sensors and Actuators, and Eurosensors IX, Stockholm, pages 312-315, a description is given of a micromirror. The micromirror is suspended from torsion springs and can be electrostatically tilted.
It is accordingly an object of the invention to provide a microrelay, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which is a component that can be used as a switch and achieves high switching speeds at a small switching voltage.
With the foregoing and other objects in view there is provided, in accordance with the invention, an electrostatically operating microrelay, comprising a substrate, a switching part movably attached on the substrate and having a side facing away from the substrate, the switching part acting as a rocker moving between two alternative switching positions, a contact electrode attached on the substrate and having two parts provided with separate electrical terminals, a contact electrode attached to the switching part, an actuator electrode disposed at the switching part and two actuator electrodes attached on the substrate. The actuator electrodes attached on the substrate are disposed relative to the actuator electrode attached to the switching part to bring about a rocking movement of the switching part into another of the two alternative switching positions by alternately applying an electric potential to the actuator electrodes attached on the substrate. The contact electrode attached on the substrate is disposed at the side of the switching part facing away from the substrate, permitting the contact electrode attached to the switching part to short the two parts of the contact electrode attached on the substrate in one of the switching positions.
Thus, the microrelay according to the invention has a switching part which is pivotably suspended on a substrate and can be moved into two alternative switching states in the manner of a rocker by electrostatic attraction through the use of suitably attached electrodes. The switching function is brought about by electrodes which are fastened to the substrate above the rocker being shorted by metallizations on the upper side of the switching part.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a microrelay, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.